As is known, dual mass flywheels are arranged between the internal combustion engine and the transmission of a motor vehicle and are provided for the purpose of increasing driving comfort. A dual mass flywheel of this kind consists essentially of a disk-shaped primary mass connected directly to the crankshaft of the internal combustion engine and of a disk-shaped secondary mass, which is arranged coaxially with said primary mass and is connected via a clutch to the input shaft of the transmission. Both masses are coupled to one another by a plurality of damping means arranged therebetween and can be twisted relative to one another, counter to the action of said damping means, by way of a friction-reducing bearing assembly arranged on a bearing flange on the primary mass. During the operation of the motor vehicle, the primary mass is actively driven by means of the rotating crankshaft of the internal combustion engine, while the secondary mass, which, for its part, drives the transmission input shaft, is taken along by way of the damping elements, by means of which the irregularities resulting from the unbalance of the moving masses in the drive train and the irregularities in the rotation of the internal combustion engine resulting from the movements of the pistons are damped.
Among the means that have proven particularly suitable for bearing support between the secondary mass and the primary mass of the dual mass flywheel are not only sliding, cylindrical roller and ball bearings, but also radial needle bearings of the kind disclosed, for example, by JP 07-279 952 A or DE 1 944 576 U. Radial needle bearings of this kind consist essentially of a thin-walled outer needle sleeve, which has radial rims, that are axially inwardly directed on both sides, a multiplicity of bearing needles rolling on the inner circumferential surface of the needle sleeve and on the outer circumferential surface of the shaft to be supported, and a needle cage, which guides the bearing needles in the circumferential direction in an evenly spaced manner. At least on one side, adjacent to the needle cage, an additional thrust washer is inserted into the needle sleeve. The washer limits the axial mobility of the needle cage together with a radial rim or a further thrust washer inserted into the needle sleeve. To seal off the needle bearing, a sealing element is furthermore arranged between the at least one thrust washer and the other radial rim. The sealing element is a metal-reinforced or, alternatively, a simple lip sealing ring composed of an elastomer. The sealing lip of the sealing element makes sliding contact with the circumferential surface of the shaft to be supported.
However, the disadvantage with radial needle bearings of this kind has proven to be the sealing thereof by means of the sliding contact between the sealing lip of the lip seal thereof and the shaft since this sliding contact usually causes high friction, as a result of which there is increased wear on the lip seal and hence a reduction in the life of the needle bearing.
One possibility of avoiding such disadvantageous sliding contact between the seal and the shaft for the purpose of sealing off a radial needle bearing has furthermore been disclosed by DE 1 869 210 U. The radial needle bearing disclosed in this publication differs essentially from the needle bearing described above in that it is designed with angular-profile thrust washers on both sides adjacent to the needle cage and that the bearing needles roll on the circumferential surface of an additional inner ring instead of on the circumferential surface of a shaft. Both thrust washers are simultaneously components of two labyrinth seals that seal off the needle bearing on both sides and are furthermore formed by the radial rims of the needle sleeve and by two additional metal sealing rings, each secured on the inner ring of the needle bearing, between the thrust washers and the radial rims. The thrust washers and the radial rims of the needle bearing each have a gap with respect to the inner ring at the inside diameter and a gap with respect to the metal sealing rings at their inner annular surface. The metal sealing rings each have a gap with respect to the thrust washers at the outside diameter, with the result that the needle bearing is sealed off on both sides by noncontact labyrinth seals, which have a sealing gap with a number of bends.
However, the disadvantage with labyrinth seals designed in this way is that, in the case of needle bearings without an inner ring, as used in support bearings in dual mass flywheels, they cannot be integrated as a modular unit into the bearing, but can only be completed when the bearing is mounted on the shaft and, thus, give rise to relatively high assembly costs.